Dental amalgam



United States Patent 2,698,231 DENTAL AMALGAM Ernst Schulze,Leverkusen-Schlebusch, and Albrecht Nehse, Leverliusen-Wiesdorf,Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft,Leverkusen, Germany, a corporation of Germany No Drawing. ApplicationMay 15, 1951, Serial No. 226,532

Claims priority, application Germany May 17, 1950 1 Claim. (Cl. 5-173)The present invention relates to a process of preparing amalgam fordental purposes.

it is an object of the present invention to prepare dental amalgam byusing a shaped unit of a dental metal powder containing a certain amountof silver and being composed of particles of different size.

A further object of the present invention is the shaped unit of theaforesaid metal powder, said shaped unit preferably consisting of acompact shaped, for instance, in tablet, pill or bar form.

Still further objects of the present invention will become apparent fromthe specification following hereafter.

It is generally recognized that the granular size of a commercial metalpowder, whether composed of filings, shavings, or millings, used in thepreparation of a dental amalgam, shall be as uniform as possible. Forinstance,

it is prescribed in the American Specification Dental Amalgam Alloy(1937) that the comminuted alloy shall be free of foreign materials andshall be uniform throughout the package. This requirement alreadyresults from the fact that separation into the component parts occurswhen packing amalgam alloys of different particle size into bottles andother vessels. The fine-grained particles settle at the bottom of thevessel whilst the coarser ones accumulate in the upper section of thevessel. Hence it follows that the coarser-grained part of the powder isused first by the dentist for preparing a dental amalgam, so that, atlast, an almost dust-like residue remains which, admixed with mercury,gives an amalgam with properties different from those of the amalgamprepared with the coarser-grained part of the metal powder. Since,furthermore, it is a commonly held opinion that a very uniformamalgamation of the small metal particles is desirable and that suchuniform amalgamation can be accomplished only by use of a metal powderof uniform granular size, dental alloys of a uniform granular size havehitherto been put on the market.

It is further known that the amalgams prepared from these metal powdersshow quite different properties, especially as to their initial andfinal hardness and expansion, and that these properties are due to themode of preparation of the amalgam from the metal powder. Experimentscarried through in connection with the present invention have shown thatthese different properties are substantially caused by the way ofgrinding the metal powder with mercury in the mortar and, furthermore,that during such grinding the extent of comminution of the metalparticles before amalgamation by the mercury plays a decisive part. Thisobservation led to investigations on the influence of the granular sizeof the metal particles and resulted in finding a handy form of a metalpowder that yields a uniform amalgam exhibiting inter alia a shortsetting time, high ultimate hardness and a controlled expansion. Forthis purpose, three requirements have to have fulfilled according to theinvention, firstly the metal powder must be prepared from an alloy witha definite silver content, secondly the metal powder must be presentduring amalgamation in different particle sizes, and thirdly a fixedweight of the metal powder must be brought into a handy shape,preferably into a compact shaped, for instance, in tablet, pill or barform, and used in this shape as a starting material for the preparationof the dental amalgam.

The metal alloy used for the preparation of dental amalgam may beobtained by milling an appropriate metal alloy. The silver content ofthis alloy substantially consisting of silver and tin shall amount to60-75%,

2,698,231 Patented Dec. 28, 1954 ice preferably to 63-67%. Besidessilver and tin the ,alloy may contain other customarily employedcomponents, such as for instance, copper and zinc. Since the largerparticles of this metal powder yield an expanding amalgam, whilst veryfine particles yield a contractin amalgam, the mixing proportion of thefiner particles and the coarser ones in the shaped unit is adjustedaccording to the present invention in such a manner that the expansioncaused by the coarser particles overbalances or at least balances thecontraction due to the finer particles. This shaped unit may, forinstance, consist of a compact shaped in tablet form which tablet can bedisintegrated by slight pressure into a granular mixture, two thirds ofwhich consist of coarser particles of which the largest ones pass asieve having 1600 meshes per square centimeter, whilst about a third ofthe total weight is present in form of particles whose individual weightcorresponds to about of that of the coarser particles. The size of themetal powder tablets, pills etc. will preferably be such, that theamalgam prepared from it suffices for one average tooth filling.

It is evident that the desired uniform final properties of the amalgamare only accomplished by constantly and accurately proportioning themetal powder and the mercury. It is, therefore, a further object of theinvention to employ the metal powder shaped, for instance, into atablet, pill, bar etc. with an accurate quantity of mercury which may bemeasured off by a special dispensing device.

As a matter of fact, the mixing of the metal powder with mercuryaccording to the invention must not result in a substantial change ofthe particle size. For this reason, after powdering the tablet etc., theblending in the mortar is to be accomplished by mere stirring only. ltis still more advisable to blend the metal powder and mercury in therubber finger stall.

The advantages attained by employing the tablets, pills etc. inaccordance with the present invention may be summarized as follows: Bycarefully measuring the ratio of the finer and coarser particles and thesilver content of the tablet, pill etc., the amalgam prepared from thisshaped unit shows a short setting time due to the finer particles, ahigh final hardness due to the coarser ones, and a controlled expansiondue to the measured proportion of the finer and coarser particles. Aconstant mixing proportion of the metal powder and mercury is achievedby using the tablets, pills etc. together with a dispensing device forthe mercury.

The invention shall be further illustrated by way of example.

Example 0.33 grain of filings of a metal alloy of 66% silver, 29% tin,3% copper and 2% zinc, two thirds of said metal alloy consisting ofcoarser grains, the larger ones of which pass a sieve having 1600 meshesper square centimeter, whilst about one third of the total quantity ofthe metal alloy is present in form of grains whose individual weightcorresponds to about of the coarser grains, are compressed into tabletsunder a pressure of 200 kg./cm. The tablets thus prepared are used asstarting material for the preparation of amalgam with the admixture ofappropriate amounts of mercury. The proportion of the filings to themercury amounts to 121.

We claim:

A process of preparing dental amalgam, which comprises forming a compactconsisting of a dental alloy powder, two-thirds of the total weight ofwhich consists of coarser particles passing a sieve having 1600 meshesper square centimeter and one-third of the total Weight of whichconsists of particles whose individual Weight corresponds to aboutone-fiftieth of that of the coarser particles, said dental alloycontaining 60-70% by Weight of silver, at least 25% of tin, not morethan 6% of copper and not more than 2% of zinc, powdering said compactunder a slight pressure corresponding to one which is exerted whenpreparing amalgam in the rubber fingerstall, whereby a dental alloypowder of different granular sizes is produced, and mixing said powderwith a measured quantity of mercury.

(References on following page) 3 References Cited in the file of thispatent UNITED STATES PATENTS 4 Number Country Date 473,381 Great BritainOct. 12, 1937 482,338 Great Britain Mar. 23, 1938 OTHER REFERENCESSmith: The Chemistry and Metallurgy of Dental Materials, pub. byBlackwell Scientific Publications, Ltd., Oxford, England, pages 98 and99.

